Couple encountered one on way north (4)
I believe the answer is:
item
'couple' is the definition.
(a romantic couple are 'an item')
'encountered one on way north' is the wordplay.
'encountered' becomes 'met' ('meet' can be a synonym of 'encounter').
'one' becomes 'i' (Roman numeral).
'on way north' says the letters should be written in reverse (in a down clue, letters go up or 'north').
'met'+'i'='meti'
'meti' reversed gives 'ITEM'.
(Other definitions for item that I've seen before include "Part of a list" , "Whole individual unit" , "Article, object" , "Object; piece" , "One article" .)